在UIPageViewController中获取用户滑动方向 [英] Get user swiping direction in UIPageViewController

问题描述

这两个方法 viewControllerBeforeViewController 和 viewControllerAfterViewController 的 UIPageViewControllerDataSource 不要告诉滑动的方向。

These two methods viewControllerBeforeViewController and viewControllerAfterViewController of the UIPageViewControllerDataSource don't tell the direction of the swipe.

的方法 transitionCompleted UIPageViewController 委托对我们也没什么帮助。它只是告诉页面是否完全刷过。

The method transitionCompleted of the UIPageViewController delegate doesn't help us much either. It just tells if the page was fully swiped.

那么我应该使用什么方法来准确检测用户方向（左或右）？

So what method should I use to detect exactly the user direction (left or right)?

这两个属性可能会有所帮助：

Probably these two properties may help:

let directionForward = UIPageViewControllerNavigationDirection.Forward
let directionReverse = UIPageViewControllerNavigationDirection.Reverse

我的代码如下所示：

import UIKit

class ProView: UIViewController, UIPageViewControllerDataSource, UIPageViewControllerDelegate {

var pageViewController: UIPageViewController?

let characterImages = ["character1", "character2", "character1", "character2", "character1", "character2", "character1", "character2"]

override func viewDidLoad() {
    super.viewDidLoad()
    createPageViewController()
    setupPageControl()

    character = 1
}

override func didReceiveMemoryWarning() {
    super.didReceiveMemoryWarning()
}

// Forward, check if this IS NOT the last controller
func pageViewController(pageViewController: UIPageViewController,
    viewControllerAfterViewController ProView: UIViewController) -> UIViewController? {

        let itemController = ProView as PageItemController

        // Check if there is another view
        if itemController.itemIndex+1 < characterImages.count {

            return getItemController(itemController.itemIndex+1)
        }

        return nil
}


// Check if this IS NOT the first controller
func pageViewController(pageViewController: UIPageViewController,
    viewControllerBeforeViewController ProView: UIViewController) -> UIViewController? {

    let itemController = ProView as PageItemController

        if itemController.itemIndex < 0 {

            return getItemController(itemController.itemIndex-1)
        }

        return nil
}

private func getItemController(itemIndex: Int) -> PageItemController? {

    if itemIndex < characterImages.count {
        let pageItemController = self.storyboard!.instantiateViewControllerWithIdentifier("ItemController") as PageItemController
        pageItemController.itemIndex = itemIndex
        pageItemController.imageName = characterImages[itemIndex]
        return pageItemController
}

    return nil
}

func createPageViewController() {

    let pageController = self.storyboard!.instantiateViewControllerWithIdentifier("PageController") as UIPageViewController
    pageController.dataSource = self
    pageController.delegate = self

    if characterImages.count > 0 {
        let firstController = getItemController(0)!
        let startingViewControllers: NSArray = [firstController]
        pageController.setViewControllers(startingViewControllers, direction: UIPageViewControllerNavigationDirection.Forward, animated: false, completion: nil)
    }

    pageViewController = pageController
    addChildViewController(pageViewController!)
    self.view.addSubview(pageViewController!.view)
    pageViewController?.didMoveToParentViewController(self)
}

func setupPageControl() {
    let appearance = UIPageControl.appearance()
    appearance.pageIndicatorTintColor = UIColor.grayColor()
    appearance.currentPageIndicatorTintColor = UIColor.whiteColor()
}

func presentationCountForPageViewController(pageViewController: UIPageViewController) -> Int {
    return characterImages.count
}

func presentationIndexForPageViewController(pageViewController: UIPageViewController) -> Int {


}

// BETA

func pageViewController(PageItemController: UIPageViewController,
    didFinishAnimating finished: Bool,
    previousViewControllers pageViewController: [AnyObject],
    transitionCompleted completed: Bool)
{

    if (!completed)
    {
        // You do nothing because whatever page you thought
        // the book was on before the gesture started is still the correct page
        return;
    }

    // This is where you would know the page number changed and handle it appropriately

    character = workaround

    }


}

class PageItemController: UIViewController {

@IBOutlet weak var imageCharacterChoose: UIImageView!

var itemIndex: Int = 0
var imageName: String = "" {
    didSet {

        if let imageView = imageCharacterChoose {imageCharacterChoose.image = UIImage(named: imageName)
        }

    }
}
}

根据pbasdf的说法，

According to what pbasdf said,

var currentIndex: Int = 0
var nextIndex: Int = 0

func pageViewController(PageItemController: UIPageViewController,
    willTransitionToViewControllers pageViewController: [AnyObject]) {

        //                          pageViewController is the pending View Controller
        nextIndex = currentIndex

        // pageViewController...... how do I get its index?
}

推荐答案

你应该同时使用 willTransitionToViewControllers：和 didFinishAnimating：委托方法来确定过渡是向前还是向后。在类的开头声明几个索引变量，例如 currentIndex 和 nextIndex （两者都是 Int ）。

You should use both the willTransitionToViewControllers: and the didFinishAnimating: delegate methods to work out whether the transition is forward or backward. Declare a couple of index variables at the start of your class, say currentIndex and nextIndex (both Int).

在 willTransitionToViewControllers 方法中，设置 nextIndex 等于挂起视图控制器的 itemIndex ：

In the willTransitionToViewControllers method, set the nextIndex equal to the itemIndex of the pending view controller:

编辑

func pageViewController(pageViewController: UIPageViewController, willTransitionToViewControllers pendingViewControllers: [AnyObject]) {
    // the page view controller is about to transition to a new page, so take note
    // of the index of the page it will display.  (We can't update our currentIndex
    // yet, because the transition might not be completed - we will check in didFinishAnimating:)
    if let itemController = pendingViewControllers[0] as? PageItemController {
        nextIndex = itemController.itemIndex
    }
}

结束编辑

此时您可以确定过渡是向前还是向后：如果 nextIndex > currentIndex ，然后转发; if nextIndex < currentIndex 然后向后。然后在 didFinishAnimating 中，如果已完成为真（因此它完成了向下一个视图控制器的转换），请设置 currentIndex 等于 nextIndex 所以你可以在任何需要的地方使用 currentIndex 指示当前屏幕上的哪个页面：

You can work out at this point whether the transition will be forward or backward: if nextIndex > currentIndex, then forward; if nextIndex < currentIndex then backward. Then in didFinishAnimating, if completed is true (so it completed the transition to the next view controller), set currentIndex equal to nextIndex so you can use currentIndex wherever you need to indicate which page is currently on screen:

编辑

func pageViewController(pageViewController: UIPageViewController, didFinishAnimating finished: Bool, previousViewControllers: [AnyObject], transitionCompleted completed: Bool) {
    if (completed) {
        // the page view controller has successfully transitioned to the next view
        // controller, so we can update our currentIndex to the value we obtained 
        // in the willTransitionToViewControllers method:
        currentIndex = nextIndex

    }
}

请注意，这些方法的第一个参数是pageViewController（UIPa的实例） geViewController），而不是当前代码中的 pageItemController 。

Note that the first argument to these methods is the pageViewController (instance of UIPageViewController), not pageItemController which you have in your current code.

最后，请注意：枚举你引用（ UIPageViewControllerNavigationDirection ）仅用于 setViewControllers（_，direction：）方法。

Finally, just to note: that enum you refer to (UIPageViewControllerNavigationDirection) is used only in the setViewControllers(_, direction:) method.

结束编辑

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